Solid state image pickup devices comprising a charge transfer device such as a charge coupled device (hereinafter referred to as a CCD) are classified broadly into the frame transfer type and the interline transfer type, and each of them is utilized in different way so as to make a good use of its advantages and features.
An example of a solid state image pickup device of the interline transfer type using a CCD is constituted as shown in FIG. 1, and comprises a photo-sensing and vertical transfer portion 3 which includes a plurality of photodetectors 1 arranged in horizontal and vertical rows and vertical transfer portions 2 each formed with a group of CCDs and provided along each of the vertical rows of the photodetectors 1, a horizontal transfer portion 4 coupled with the photo-sensing and vertical transfer portion 3 and an output portion 5 coupled with the horizontal transfer portion 4 and provided with a signal output terminal 5a, the whole of which are formed on a common semiconductor substrate.
In a solid state image pickup apparatus employing such a solid state image pickup device as mentioned above, a predetermined vertical transfer driving signal and a predetermined horizontal transfer driving signal are applied to the vertical transfer portions 2 and the horizontal transfer portion 4, respectively, so that vertical and horizontal charge transfers are performed in the solid state image pickup device. With such driving signals, signal charge obtained in the photodetectors 1 in response to the light received thereby during for example, one frame period is read out to the vertical transfer portions 2 and then transferred vertically toward the horizontal transfer portion 4 by the charge transfer operation of the vertical transfer portions 2 during each horizontal blanking period so that the signal charge produced in each horizontal row of the photodetectors 1 is transferred in turn to the horizontal transfer portion 4. The signal charge transferred to the horizontal transfer portion 4 is further transferred horizontally to the output portion 5 by the charge transfer operation of the horizontal transfer portion 4 during each horizontal video period and as a result of this an image pickup signal output is obtained at the signal output terminal 5a.
The photo-sensing and vertical transfer portion 3 mentioned above contains transfer gate areas 6 provided between each vertical row of the photodetectors 1 and the corresponding one of the vertical transfer portions 2, and a channel stop area 7 and an overflow control gate portion 8 provided around each of the photodetectors 1, as shown in FIG. 2. Further, an overflow drains 9 is provided contiguous to each of the overflow control gate portions 8, and each of the overflow drains 9 and the corresponding one of the vertical transfer portions 2 are separated by a channel stop area 10. The above mentioned various areas and portions are covered by insulating layer, and on the insulating layer, vertical transfer electrodes .phi..sub.1 and .phi..sub.2 each elongated in the horizontal direction are provided alternately in the vertical direction in the areas corresponding to the vertical transfer portions 2. Each vertical transfer electrode .phi..sub.1 is composed of a charge storage electrode .phi..sub.1c and a charge transfer electrode (potential barrier electrode) .phi..sub.1t, and each vertical transfer electrode .phi..sub.2 is composed of a charge storage electrode .phi..sub.2c and a charge transfer electrode .phi..sub.2t. In the vertical transfer portions 2, storage regions are formed under the charge storage electrodes .phi..sub.1c and .phi..sub.2c and transfer regions (potential barrier regions) are formed under the charge transfer electrodes .phi..sub.1t and .phi..sub.2t, and each transfer region is subjected to ion implantation or is provided thereon with a thick insulating layer so as to have a potential well which is shallower (lower) than that of the storage region adjacent thereto and so as to form a potential barrier. Further, a transfer gate electrode T which extends in the vertical direction is provided on each group of the transfer gate areas 6 the electrode T is aligned in the vertical direction. An overflow control gate electrode OG which also extends in the vertical direction is provided on each overflow control gate portion 8. A light shielding layer 11 is also provided on the above mentioned various areas and portions except the areas of the photodetectors 1 so as to form a light shielded portion.
In the photo-sensing and vertical transfer portion 3 of the solid state image pickup device of the interline transfer type which uses the CCD described, a predetermined gating signal .phi..sub.t is supplied to the transfer gate electrodes T so that a transfer gate voltage is applied selectively to the transfer gate areas 6, and a predetermined bias voltage is supplied through the overflow control gate electrodes OG to the overflow control gate portions 8. Then, the vertical transfer electrodes .phi..sub.1 and .phi..sub.2 are supplied with two phase driving signals .phi..sub.1 and .phi..sub.2, respectively, and the voltages of these driving signals .phi..sub.1 and .phi..sub.2 are applied to the vertical transfer portions 2 positioned under the vertical transfer electrodes .phi..sub.1 and .phi..sub.2. With the driving signals .phi..sub.1 and .phi..sub.2, signal charges which are stored in the photodetectors 1 are read out through the transfer gate areas 6 to the vertical transfer portions 2 during every field period, for example, and the signal charges read out to the vertical transfer portions 2 are transferred vertically to the horizontal transfer portion 4 during each period corresponding to the horizontal blanking period.
When the previously proposed solid state image pickup device of the interline transfer type using the CCD which has a photo-sensing and vertical transfer portion 3 such as described above is in operation for producing an image pickup signal output, the light receiving portion upon which the light from an object is received is limited to the area of the photodetectors on which the light shielding layer is not provided and therefore the light receiving aperture, ratio, that is, the ratio of the area of the part of the aperture for receiving the light to the area of the whole photo-sensing and vertical transfer portion 3 is quite low. Consequently, the photosensitivity of the device is low, and especially, in the case of operation for producing an image pickup signal output representing a still image in which the light is received during the short period in which a shutter mechanism which is provided over the photo-sensing and vertical transfer portion 3 is open. The image pickup output signal is obtained in response to the signal charge stored in the photodiodes 1 during such short period, and an image pickup signal output having sufficient dynamic range and with a high signal to noise ratio can not be obtained.